ARP-catch
1997 Thomas H. Ptacek
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This is a 4.4BSD program that implements, in userland, third-party
proxy ARP. In a nutshell, this lets you proxy-ARP an arbitrary IP
address to an arbitrary MAC address, from any machine on the network.
This is useful if your router doesn't do proxy ARP, or does it only
in an all-or-none fashion.

This code will not work outside of 4.4BSD (it relies on BPF). Furthermore,
it won't run on most 4.4BSD operating systems, because a problem with the
standard BPF implementation (try spoofing your source ethernet frame
address on NetBSD). I've made available an LKM that "fixes" the problem on
FreeBSD 3.0; you can find it at http://www.enteract.com/~tqbf.

There's not much to document here. The program is a daemon, and reads 
a config file. The config file consists of "router" and "proxy" lines; a
"router" line gives a symbolic name for a MAC address, ie:

router gateway de:ad:be:ef:ca:fe

... and a "proxy" line maps an IP address to a router name or a MAC
address, ie:

proxy 10.100.200.1 gateway
proxy 10.100.200.2 ab:ad:ca:fe:00:11

This is fairly esoteric stuff; read the code if you need to know more.

If you have problems, questions, comments, bitches, etc, feel free to mail
me at <tqbf@secnet.com>
